1) Field of the Invention
The invention relates to a method for encapsulating electronic components in a mould. The invention also relates to a device for encapsulating an electronic component, in particular a semiconductor, with encapsulating material.
2) Description of the Prior Art
The encapsulating of electronic components, such as semiconductor circuits in particular, is applied on large scale. The electronic components are here usually mounted on a carrier (“leadframe”, “board”) and such a carrier is clamped between mould parts such that a mould cavity is defined around electronic components mounted on the carrier. An important consideration here is that the adhesion of the encapsulating material to the mould during curing of the encapsulating material must remain limited so as to thus prevent damage to the encapsulated products and to prevent contamination of the mould. There are various solutions for limiting the degree of adhesion between encapsulating material and mould. Use can thus be made of a layer of foil material separating the encapsulating material and the mould. This solution is expensive and not possible for all mould embodiments. Another solution employed on a large scale heretofore is to provide a mould part, optionally locally, with a specific coating (for instance a coating with an increased concentration of Cr and/or TiN) optionally in combination with the application of a temporary coating (such as a wax layer). At first use or after a period of standstill mould parts are in practice first conditioned by carrying out some dummy encapsulating runs such that conditioning material from the encapsulating material leaves a (temporary) coating on a mould part during these dummy encapsulating runs. When there is an undesirable increase in the adhesion between the encapsulating material and a mould part during performing of successive encapsulating operations, the usual option is to take the mould part or parts out of production for a time and to clean the mould parts for a longer period with a specific cleaning material (such as for instance melamine). The existing solutions for limiting the adhesion between encapsulating material and mould part, with methods and in devices as described in the preamble, are: that the adhesion can still develop undesirably high values, that the process of the increase of the adhesion during use is not wholly predictable and understandable, that mould parts are unusable for part of the time and that production losses occur.
The Japanese patent JP 03 281210 describes a method for encapsulating an electronic component with resin, wherein the encapsulating process takes place in an inert gas environment. It is thus possible to prevent air inclusions occurring in the encapsulating material and the surface of an moulded housing being provided with recesses or fragmented parts. Use is made here particularly of a nitrogen atmosphere.
Japanese patent JP 02 156644 discloses a method to release an encapsulated semiconductor device from a metal mould cavity, wherein an ejector pin is used to eject a moulded part from the cavity. A gas, such as air, nitrogen or the like is additionally discharged directly into the cavity through a blow-off port, positioned immediately adjacent to the ejector pin.
Japanese patent 2000 263603 discloses a device and method to release a moulding from a mould without cracking. The disclosed device comprises a channel, which terminates directly into the mould cavity and through which resin can be sucked into the mould cavity. After moulding, the same channel is used to introduce compressed air into the mould cavity to release the moulding from the mould.
The object of the present invention is to provide an improved method and device for encapsulating electronic components in a mould, with which the problems resulting from adhesion between mould and encapsulating material can be limited.